This invention relates to a container for a metal-air battery.
Batteries are commonly used electrical energy sources. A battery contains a negative electrode, typically called the anode, and a positive electrode, typically called the cathode. The anode contains an active material that can be oxidized; the cathode contains or consumes an active material that can be reduced. The anode active material is capable of reducing the cathode active material. In order to prevent direct reaction of the anode material and the cathode material, the anode and the cathode are electrically isolated from each other by a separator.
When a battery is used as an electrical energy source in a device, such as a cellular telephone, electrical contact is made to the anode and the cathode, allowing electrons to flow through the device and permitting the respective oxidation and reduction reactions to occur to provide electrical power. An electrolyte in contact with the anode and the cathode contains ions that flow through the separator between the electrodes to maintain charge balance throughout the battery during discharge.
In a metal-air electrochemical cell, oxygen is reduced at the cathode, and a metal is oxidized at the anode. Oxygen is supplied to the cathode from the atmospheric air external to the cell through one or more air access port(s) in the cell container.
During high rate discharge conditions, the flow of air across the cathode is not always uniform. Instead, the areas of the cathode closest to the air access ports can be over-utilized, while the areas of the cathode that are farther away from the air access ports can be under-utilized. Uneven use of the cathode can lead to poor battery performance and reduced battery life.
The battery of the invention has membrane having a variable thickness. The variable thickness of the membrane helps to distribute the air evenly to all parts of the cathode surface.
In one aspect, the invention features a metal-air battery having (a) a container having at least one air access port; (b) an anode; (c) a cathode; (d) a separator between the anode and the cathode; and (e) a membrane between the cathode and the container. The membrane has a variable thickness.
For example, a portion of the membrane adjacent to the air access port can be thicker than a portion of the membrane that is not adjacent to the air access port or a portion of the membrane can be compressed relative to its original thickness while another portion of the membrane is not compressed. These configurations provide air diffusion paths of relatively uniform lengths to all portions of the cathode. The air access port can be a louver, which can provide air flow to large portions of the cathode surface, while maintaining the structural integrity of the battery container.
In another aspect, the invention features a method of controlling air flow to a cathode in a metal-air battery. The process includes (a) covering a cathode with a membrane, the membrane having a variable thickness, and (b) inserting the cathode and the membrane into a container having at least one air access port.
The method allows for controlling air flow to the cathode, which can be regulated, in part, by arranging a variable thickness membrane between an air access port and the cathode. The variable thickness membrane distributes air flow evenly to the cathode, for example, by providing air diffusion paths of relatively uniform lengths to all portions of the cathode. The discharge performance of the battery can be improved by controlling the air flow to the cathode.
As used herein, xe2x80x9cadjacentxe2x80x9d means within 0.5 mm of the air access port.
As used herein, xe2x80x9cvariable thicknessxe2x80x9d means that a first portion of the membrane has a thickness that is at least 12% thinner than the thickness of a second portion of the membrane.
As used herein, xe2x80x9ccompressedxe2x80x9d means that a portion of the membrane compressed to reduce the number of pores in that portion of the membrane and xe2x80x9cnot compressedxe2x80x9d means that the membrane thickness is at least 80% of the original membrane thickness.
As used herein, a xe2x80x9clouverxe2x80x9d means an opening or openings, having a leaf or tab, through which air can flow. When the louver is open on one side, the leaf is slanted. When the louver is open on both sides, the tab is substantially parallel to the outer surface of the container.
As used herein, a xe2x80x9clouver openingxe2x80x9d means the distance between the can and the edge of the leaf or tab of a louver.
As used herein, the xe2x80x9clouver open areaxe2x80x9d means the length of the louver times the width of the louver opening, or openings in the case of louvers open on two sides.
Other features and advantages of the invention will be apparent from the description of the preferred embodiment thereof, and from the claims.